The Preamble to the Constitution provides one way of answering this question as to the moral duty of Congress to the American people. Congress is to be part of the process by which we “form a more perfect union, establish justice, insure domestic tranquility, provide for the common defense, promote the general welfare and secure the blessings of liberty to us and our posterity.” That job is entrusted to them as a body. Shutting down the government and threatening the full faith and credit of the United States of America does none of those things and indeed undermines them.
Another way of looking at the question is this: it is pretty clear that leadership matters, and at times it matters a lot. A dysfunctional and ideologically-polarized Congress will tend to increase, rather than decrease, the level of tension and polarization within the country. A Congress that works together will tend to decrease that level of tension and polarization. We all know this. The moral duty of Congress, therefore, is to model a functional government that recognizes it will never serve the needs of the people perfectly, but always seeks, together, to serve the needs of the people as best as they can in the moment they have. Congress is not doing that duty.
In summary, Congress has two moral duties: keep the country stable by modeling cooperation and fulfill as best they can the mandate of the Preamble. They are doing neither right now. At Gettysburg, Lincoln told the assembled crowd that it was up to the Union forces to see that “government of the people, by the people and for the people shall not perish from the earth.” This Congress is flirting with the idea that ideological purity is more important than this great goal. This Congress is wrong.
Thank you Bill, for putting it so well.
Anna